java - 了解执行 Google Datastore 查询时的 "CancellationException: Task was cancelled"错误

Question

我使用的是 Google App Engine 1.9.48 版。在一些数据存储查询期间，我随机收到“CancellationException:任务已取消”错误。而且我不太确定到底是什么导致了这个错误。来自 other堆栈溢出posts ，我隐约明白这与超时有关，但不完全确定是什么原因造成的。我没有使用任何任务队列 - 如果有帮助的话。

下面是堆栈跟踪:

java.util.concurrent.CancellationException: Task was cancelled.
    at com.google.common.util.concurrent.AbstractFuture.cancellationExceptionWithCause(AbstractFuture.java:1126)
    at com.google.common.util.concurrent.AbstractFuture.getDoneValue(AbstractFuture.java:504)
    at com.google.common.util.concurrent.AbstractFuture.get(AbstractFuture.java:407)
    at com.google.common.util.concurrent.AbstractFuture$TrustedFuture.get(AbstractFuture.java:86)
    ....
    at com.sun.proxy.$Proxy14.size(Unknown Source)
    at main.java.com.continentalist.app.model.Model.getEntitySentimentCounts(Model.java:285)
    at main.java.com.continentalist.app.model.Model.access$100(Model.java:37)
    at main.java.com.continentalist.app.model.Model$2.vrun(Model.java:251)
    at com.googlecode.objectify.VoidWork.run(VoidWork.java:14)
    at com.googlecode.objectify.VoidWork.run(VoidWork.java:11)
    at com.googlecode.objectify.ObjectifyService.run(ObjectifyService.java:81)
    ...

引发该错误的我的应用程序引擎代码位于此处。我在抛出错误的地方添加了行注释(通常在 list().size() 之一):

private EntityAnalysis getEntitySentimentCounts(ComboCall comboCall) {
        Query<ObjectifyArticle> queryArticles = ofy().load().type(ObjectifyArticle.class);

        queryArticles = queryArticles.filter("domain", comboCall.getDomain());

        Set<Entity> entitySet = comboCall.getEntitySet();
        SentimentCount[] allSentimentCounts = new SentimentCount[entitySet.size()];
        int index = 0;
        for(Entity eachEntity : entitySet) {
            SentimentCount sentimentCount = new SentimentCount();
            String eachEntityName = eachEntity.getText();
            Query<ObjectifyArticle> newQuery = queryArticles;
            newQuery = newQuery.filter("entityName", eachEntityName);
            sentimentCount.setEntityName(eachEntityName);   

            Query<ObjectifyArticle> positiveFilter = newQuery;
            positiveFilter = positiveFilter.filter("entityType", POSITIVE);
            int positive = positiveFilter.list().size(); // ERROR EITHER HERE
            sentimentCount.setPositiveCount(positive+"");

            Query<ObjectifyArticle> negativeFilter = newQuery;
            negativeFilter = negativeFilter.filter("entityType", NEGATIVE);
            int negative = negativeFilter.list().size();  // OR HERE
            sentimentCount.setNegativeCount(""+negative);

            Query<ObjectifyArticle> neutralFilter = newQuery;
            neutralFilter = neutralFilter.filter("entityType", NEUTRAL);
            int neutral = neutralFilter.list().size();   // OR HERE
            sentimentCount.setNeutralCount(""+neutral);

            allSentimentCounts[index] = sentimentCount;
            index++;
        }
        EntityAnalysis entityAnalysis = new EntityAnalysis();
        entityAnalysis.setDomain(comboCall.getDomain());
        entityAnalysis.setSentimentCount(allSentimentCounts);
        return entityAnalysis;
    }

Answer 1

1. 您不需要调用.list().size()，您只需调用count()即可。

2. 如果您只是进行计数，请使用仅键查询 - 它是免费的并且速度更快。

3. 当您希望处理大量实体时，不要忘记在查询中设置 chunkAll()。它比默认设置快得多。

如果您仍然遇到这些异常，则需要在查询中使用游标。